Polyester has long been recognized as a desirable material for textile applications. The basic processes for the manufacture of polyester are relatively well known and straight forward, and fibers from polyester can be appropriately woven or knitted to form textile fabric. Polyester fibers can be blended with other fibers such as wool or cotton to produce fabrics which have the enhanced strength, durability and memory aspects of polyester, while retaining many of the desired qualities of the natural fiber with which the polyester is blended.
As with any fiber, the particular polyester fiber from which any given fabric is formed must have properties suitable for manufacture, finishing, and end use of that fabric. Typical applications include both ring and open-end spinning, either with or without a blended natural fiber, weaving or knitting, dyeing and finishing. In addition, it has long been known that synthetic fibers such as polyester which are initially formed as extruded linear filaments will exhibit more of the properties of natural fibers such as wool or cotton if they are treated in some manner which changes the linear filament into some other shape. Such treatments are generally referred to in the art as texturizing, and can include false twisting, crimping and certain chemical treatments.
In a homopolymeric state, polyester exhibits good strength characteristics. Typical measured strength characteristics include tenacity, which is generally expressed as the grams per denier required to break a filament, and the modulus, which refers to the filament strength at a specified elongation ("SASE"). Tenacity and modulus are also referred to together as the tensile characteristics or "tensiles" of a given fiber. In relatively pure homopolymeric polyester, the tenacity will generally range from about 4.5 to about 7 g/denier.
In many applications, of course, it is desirable that the textile fabric be available in a variety of colors, accomplished by a dyeing step. Substantially pure polyester, however, is not as dyeable as most natural fibers, or as would otherwise be desired, and therefore must usually be dyed under conditions of high temperature, high pressure, or both, or at atmospheric conditions with or without the use of swelling agents, commonly referred to as "carriers". Accordingly, various techniques have been developed for enhancing the dyeability of polyester.
One technique for enhancing the dyeability of polyester is the addition of various functional groups to the polymer to which dye molecules or particles such as pigments attach more readily, either chemically or physically, depending upon the type of dyeing technique employed. Common types of additives include molecules with functional groups that tend to be more receptive to chemical reaction with dye molecules than polyester. These often include carboxylic acids (particularly dicarboxylic or other multifunctional acids), and organometalic sulfate or sulfonate compounds.
It is known in the art that adipic acid can be added to terephthlatic acid (TA) or dimethyl terephthalate (DMT) to produce a polyester with improved dyeability properties of the fibers. Adding increased amounts of adipic acid during production of polyester will increase the dyeability of the resulting fiber. However, there are a number of disadvantages associated with the addition of adipic acid for the purposes of enhancing dyeability. These disadvantages are shown in the loss of strength of the fiber as indicated by the lower modulus and tenacity measurement of the fiber.
It is also known in the art that pentaerythritol at low levels of less than about 450 ppm by weight of the TA or DMT can be incorporated into polyester for providing improved strength of the fiber including the modulus and tenacity of the fiber. However, at levels of greater than 450 ppm, the pentaerythritol may result in decreased strength and dyeability of the fiber. U.S. Pat. No. 4,113,704 to MacLean et al discloses use of pentaerythritol as a branching agent to enhance dyeability within a limited range and also to enhance the productivity of polyester.
It is also known that polyethylene glycol (PEG) can offer various advantages when incorporated into polyester for textile fibers, including improved dyeing characteristics. Nevertheless, there are a number of disadvantages associated with the application of PEG to polyester as in the case of adding adipic acid to the polyester, in particular, the diminished strength of the fiber.
Accordingly, there remains a need to develop a suitable additive for polyester fibers that enhance the dyeing properties of the polyester fiber while also enhancing such characteristics as strength, hot air shrinkage (HAS), and dyeability.